This invention relates to the tape recording parts, and, more particularly, to an improved braking system for a reel-to-reel tape transport.
Braking systems for reel-to-reel magnetic tape transports may be generally categorized as either dynamic or mechanical.
Dynamic (or electrical) braking systems employ a braking current passed through the motor windings to provide braking action. This braking current is usually d-c although some systems employ "reverse-torque" a-c braking current. The braking action must be differential with the greater drag imposed on the payout reel to avoid tape spillage. Once the proper currents have been established for the reel motors for various braking conditions, this form of braking is highly reliable since no friction involving mechanical parts need be considered, the braking action being obtained from electro-magnetic fields. There are, however, two inherent problems associated with the use of dynamic braking when conventional a-c reel drive motors are employed. First, braking action is proportional to the angular speed of the motor and is therefore high when the motor is rotating at a high speed and drops to a very low value when the motor is stopped, thus, giving very poor holding action. Second, the amount of braking current required for smooth and rapid braking action frequently causes overheating of the motor if left on for extended periods to obtain holding action while the reels are stopped.
Mechanical braking systems are commonly used in reel-to-reel recording equipment and normally consist of a brake drum or hub attached to each reel drive shaft, together with a brake band or pad which can be brought to bear against the drum surface to provide stopping action due to friction. To avoid spilling or breaking the tape, the decelerating action, as with dynamic braking, must be differential; that is, it must provide more braking action on the reel which is paying out tape than on the reel which is taking up. This requirement mandates careful mechanical adjustment to insure proper operation. Practically, however, each time the brakes are applied, there is friction wear between the drum and the brake band or pad surface which results in continuously changing braking characteristics. In addition, the friction characteristics can vary with temperature and humidity, thus giving inconsistent braking action. In practice, mechanical braking systems require periodic adjustment and replacement of friction-worn parts. They do, however, provide good holding action when the reels are not turning.
Those skilled in the art will appreciate that it would be highly desirable to provide a reel-to-reel tape transport having a braking system employing the best characteristics of both dynamic and mechanical braking while avoiding the drawbacks of each, and it is to that end that my invention is directed.
It is therefore a broad object of my invention to provide an improved braking system for a reel-to-reel magnetic tape transport.
It is another object of my invention to provide a braking system for a tape transport which combines the best characteristics of dynamic and mechanical braking.
It is yet another object of my invention to provide unique mechanical braking means for a magnetic tape transport which is employed in conjunction with a dynamic braking system and which takes over the function of the dynamic braking system upon loss of power.
In a more specific aspect, it is an object of my invention to provide a combination dynamic and mechanical braking system for a magnetic tape transport wherein the mechanical braking sub-system, by virtue of its shape and disposition of brake pads carried by pivoted arms disposed proximate payoff and take-up reels, obtains differential braking according to the tape direction.